1. Field of the Invention
The present invention relates to a dehydrating concentrator for separating waste paper pulp slurry or other industrial waste slurry into moisture and solid components or into moisture components and concentrated stock.
2. Description of the Related Art
In paper pulp industry, pulp stock with low concentration is often concentrated to have higher concentration. When paper pulp stock is to be concentrated to a concentration of for example 30% (moisture content 70%) or more by a screw thickener, stock to be processed must be set to have a concentration of for example 2.5% or more so that stock suspension has lower fluidity. This is because paper pulp stock in general has a strong water-retaining property and requires high pressure applied so as to be concentrated to a concentration of for example 30% or more. Application of high pressure to the suspension of stock to be processed and having high fluidity would fail since such stock suspension with high fluidity might escape even through a minute gap.
On the other hand, even a strainer with larger pores can apply high pressure to stock suspension and readily concentrate it into a higher concentration provided that the stock suspension to be processed is pre-concentrated to have low fluidity since pulp fibers can form a very dense and compact mat by itself on the surface of the strainer. Several types of apparatuses including a screw thickener as described above are known as systems utilizing this principle.
As a dehydrating concentrator utilizing centrifugal force, a centrifugal separator is known. This is an apparatus which applies high centrifugal force on a suspension containing solid components to remove moisture or water components through a strainer. The resultant dehydrated stock is discharged by a screw which scrapes off the stock on an inner surface of the strainer.
In the case of the screw thickener mentioned above, sufficient dehydration cannot be attained unless stock to be processed has a concentration of for example 2.5% or more. Moreover, solid components tend to admix in the stock solution after squeezing since the strainer cannot be made to have pores with a diameter smaller than a predetermined value (e.g., 2 mm in diameter). In the case of the centrifugal separator, a drive for the separator must be sturdy in structure since sufficient dehydration effect cannot be attained unless the centrifugal force applied to the stock is 1000 G or more. Moreover, during hydration, fibers of pulp stock tend to be entangled with each other into a thick stock mat which may be rotated together with the screw, resulting in failure of smooth discharge of the dehydrated stock.